Re-land: Implement ObservedArrayPop, ObservedArrayShift, ObservedArrayUnshift & ObservedArraySplice

src/array.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 377 matching lines @@
     separator = NonStringToString(separator);
   }
 
   var result = %_FastAsciiArrayJoin(this, separator);
   if (!IS_UNDEFINED(result)) return result;
 
   return Join(this, length, separator, ConvertToString);
 }
 
 
+function ObservedArrayPop(n) {
+  n--;
+  var value = this[n];
+
+  EnqueueSpliceRecord(this, n, [value], 1, 0);
+
+  try {
+    BeginPerformSplice(this);
+    delete this[n];
+    this.length = n;
+  } finally {
+    EndPerformSplice(this);
+  }
+
+  return value;
+}
+
 // Removes the last element from the array and returns it. See
 // ECMA-262, section 15.4.4.6.
 function ArrayPop() {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.pop"]);
   }
 
   var n = TO_UINT32(this.length);
   if (n == 0) {
     this.length = n;
     return;
   }
+
+  if (%IsObserved(this))
+    return ObservedArrayPop.call(this, n);
+
   n--;
   var value = this[n];
   delete this[n];
   this.length = n;
   return value;
 }
 
 
 function ObservedArrayPush() {
   var n = TO_UINT32(this.length);
   var m = %_ArgumentsLength();
 
   EnqueueSpliceRecord(this, n, [], 0, m);
 
   try {
     BeginPerformSplice(this);
-
     for (var i = 0; i < m; i++) {
       this[i+n] = %_Arguments(i);
     }
     this.length = n + m;
   } finally {
     EndPerformSplice(this);
   }
 
   return this.length;
 }
@@ skipping 113 matching lines @@
       if (!IS_UNDEFINED(current_j) || j in this) {
         this[i] = current_j;
         delete this[j];
       }
     }
   }
   return this;
 }
 
 
+function ObservedArrayShift(len) {
+  var first = this[0];
+
+  EnqueueSpliceRecord(this, 0, [first], 1, 0);
+
+  try {
+    BeginPerformSplice(this);
+    SimpleMove(this, 0, 1, len, 0);
+    this.length = len - 1;
+  } finally {
+    EndPerformSplice(this);
+  }
+
+  return first;
+}
+
 function ArrayShift() {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.shift"]);
   }
 
   var len = TO_UINT32(this.length);
 
   if (len === 0) {
     this.length = 0;
     return;
   }
 
+  if (%IsObserved(this))
+    return ObservedArrayShift.call(this, len);
+
   var first = this[0];
 
-  if (IS_ARRAY(this) && !%IsObserved(this)) {
+  if (IS_ARRAY(this)) {
     SmartMove(this, 0, 1, len, 0);
   } else {
     SimpleMove(this, 0, 1, len, 0);
   }
 
   this.length = len - 1;
 
   return first;
 }
 
+function ObservedArrayUnshift() {
+  var len = TO_UINT32(this.length);
+  var num_arguments = %_ArgumentsLength();
+
+  EnqueueSpliceRecord(this, 0, [], 0, num_arguments);
+
+  try {
+    BeginPerformSplice(this);
+    SimpleMove(this, 0, 0, len, num_arguments);
+    for (var i = 0; i < num_arguments; i++) {
+      this[i] = %_Arguments(i);
+    }
+    this.length = len + num_arguments;
+  } finally {
+    EndPerformSplice(this);
+  }
+
+  return len + num_arguments;
+}
 
 function ArrayUnshift(arg1) {  // length == 1
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.unshift"]);
   }
 
+  if (%IsObserved(this))
+    return ObservedArrayUnshift.apply(this, arguments);
+
   var len = TO_UINT32(this.length);
   var num_arguments = %_ArgumentsLength();
 
-  if (IS_ARRAY(this) && !%IsObserved(this)) {
+  if (IS_ARRAY(this)) {
     SmartMove(this, 0, 0, len, num_arguments);
   } else {
     SimpleMove(this, 0, 0, len, num_arguments);
   }
 
   for (var i = 0; i < num_arguments; i++) {
     this[i] = %_Arguments(i);
   }
 
   this.length = len + num_arguments;
@@ skipping 40 matching lines @@
   } else {
     SimpleSlice(this, start_i, end_i - start_i, len, result);
   }
 
   result.length = end_i - start_i;
 
   return result;
 }
 
 
+function ComputeSpliceStartIndex(start_i, len) {
+  if (start_i < 0) {
+    start_i += len;
+    return start_i < 0 ? 0 : start_i;
+  }
+
+  return start_i > len ? len : start_i;
+}
+
+
+function ComputeSpliceDeleteCount(delete_count, num_arguments, len, start_i) {
+  // SpiderMonkey, TraceMonkey and JSC treat the case where no delete count is
+  // given as a request to delete all the elements from the start.
+  // And it differs from the case of undefined delete count.
+  // This does not follow ECMA-262, but we do the same for
+  // compatibility.
+  var del_count = 0;
+  if (num_arguments == 1)
+    return len - start_i;
+
+  del_count = TO_INTEGER(delete_count);
+  if (del_count < 0)
+    return 0;
+
+  if (del_count > len - start_i)
+    return len - start_i;
+
+  return del_count;
+}
+
+
+function ObservedArraySplice(start, delete_count) {
+  var num_arguments = %_ArgumentsLength();
+  var len = TO_UINT32(this.length);
+  var start_i = ComputeSpliceStartIndex(TO_INTEGER(start), len);
+  var del_count = ComputeSpliceDeleteCount(delete_count, num_arguments, len,
+                                           start_i);
+  var deleted_elements = [];
+  deleted_elements.length = del_count;
+  var num_elements_to_add = num_arguments > 2 ? num_arguments - 2 : 0;
+
+  try {
+    BeginPerformSplice(this);
+
+    SimpleSlice(this, start_i, del_count, len, deleted_elements);
+    SimpleMove(this, start_i, del_count, len, num_elements_to_add);
+
+    // Insert the arguments into the resulting array in
+    // place of the deleted elements.
+    var i = start_i;
+    var arguments_index = 2;
+    var arguments_length = %_ArgumentsLength();
+    while (arguments_index < arguments_length) {
+      this[i++] = %_Arguments(arguments_index++);
+    }
+    this.length = len - del_count + num_elements_to_add;
+
+  } finally {
+    EndPerformSplice(this);
+    if (deleted_elements.length || num_elements_to_add) {
+       EnqueueSpliceRecord(this,
+                           start_i,
+                           deleted_elements.slice(),
+                           deleted_elements.length,
+                           num_elements_to_add);
+    }
+  }
+
+  // Return the deleted elements.
+  return deleted_elements;
+}
+
+
 function ArraySplice(start, delete_count) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.splice"]);
   }
 
+  if (%IsObserved(this))
+    return ObservedArraySplice.apply(this, arguments);
+
   var num_arguments = %_ArgumentsLength();
-
   var len = TO_UINT32(this.length);
-  var start_i = TO_INTEGER(start);
-
-  if (start_i < 0) {
-    start_i += len;
-    if (start_i < 0) start_i = 0;
-  } else {
-    if (start_i > len) start_i = len;
-  }
-
-  // SpiderMonkey, TraceMonkey and JSC treat the case where no delete count is
-  // given as a request to delete all the elements from the start.
-  // And it differs from the case of undefined delete count.
-  // This does not follow ECMA-262, but we do the same for
-  // compatibility.
-  var del_count = 0;
-  if (num_arguments == 1) {
-    del_count = len - start_i;
-  } else {
-    del_count = TO_INTEGER(delete_count);
-    if (del_count < 0) del_count = 0;
-    if (del_count > len - start_i) del_count = len - start_i;
-  }
-
+  var start_i = ComputeSpliceStartIndex(TO_INTEGER(start), len);
+  var del_count = ComputeSpliceDeleteCount(delete_count, num_arguments, len,
+                                           start_i);
   var deleted_elements = [];
   deleted_elements.length = del_count;
-
-  // Number of elements to add.
-  var num_additional_args = 0;
-  if (num_arguments > 2) {
-    num_additional_args = num_arguments - 2;
-  }
+  var num_elements_to_add = num_arguments > 2 ? num_arguments - 2 : 0;
 
   var use_simple_splice = true;
-
   if (IS_ARRAY(this) &&
-      !%IsObserved(this) &&
-      num_additional_args !== del_count) {
+      num_elements_to_add !== del_count) {
     // If we are only deleting/moving a few things near the end of the
     // array then the simple version is going to be faster, because it
     // doesn't touch most of the array.
     var estimated_non_hole_elements = %EstimateNumberOfElements(this);
     if (len > 20 && (estimated_non_hole_elements >> 2) < (len - start_i)) {
       use_simple_splice = false;
     }
   }
 
   if (use_simple_splice) {
     SimpleSlice(this, start_i, del_count, len, deleted_elements);
-    SimpleMove(this, start_i, del_count, len, num_additional_args);
+    SimpleMove(this, start_i, del_count, len, num_elements_to_add);
   } else {
     SmartSlice(this, start_i, del_count, len, deleted_elements);
-    SmartMove(this, start_i, del_count, len, num_additional_args);
+    SmartMove(this, start_i, del_count, len, num_elements_to_add);
   }
 
   // Insert the arguments into the resulting array in
   // place of the deleted elements.
   var i = start_i;
   var arguments_index = 2;
   var arguments_length = %_ArgumentsLength();
   while (arguments_index < arguments_length) {
     this[i++] = %_Arguments(arguments_index++);
   }
-  this.length = len - del_count + num_additional_args;
+  this.length = len - del_count + num_elements_to_add;
 
   // Return the deleted elements.
   return deleted_elements;
 }
 
 
 function ArraySort(comparefn) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.sort"]);
@@ skipping 808 matching lines @@
   ));
 
   SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();